The photochemical conversion of sterols in skin to carcinogenic chemicals has been suggested as a possible explanation for the carcinogenic activity of ultraviolet light (UVL). Since the demonstration of the occurrence of a naturally occuring carcinogenic sterol in UVL-irradiated skin, this laboratory's efforts have centered around the elucidation of the role this compound plays in the development of actinic skin cancer. During the course of these studies, a mixture of dietarily supplemented antioxidants were shown to not only inhibit the formation of the carcinogenic sterol but to markedly suppress the formation and development of UVL-induced tumors as well. In view of the prophylactic potential of dietary antioxidants and their usefulness as a tool to discern the role of photochemical products in the etiology of UVL-induced cancer, this proposal seeks to: (1) determine the most efficacious antioxidants in tumor suppression; (2) the minimal levels of antioxidants required to significantly suppress tumor formation and whether such suppression involves tumor initiation, developmental stages, or both; (3) determine whether tumor suppression by antioxidants is mediated by an umbrageous or physiological response and (4) examine the role sterol epoxide metabolites play in UVL-induced tumor development.